1. Field of the Invention:
The present invention relates to a method for the manufacture of a fiber reinforced resin structure which is formed of a long continuous fiber strand impregnated with resin, and particularly to a method for the reinforcement of branched parts of a long continuous fiber reinforced resin structure, to a steering wheel core member formed from a long continuous fiber reinforced resin having the branched parts thereof reinforced, and to a method for the manufacture of the steering wheel core member.
2. Description of the Background:
Fiber reinforced resin structures which use a long continuous fiber strand have various advantages such as light weight, high strength, resistance to corrosion, and freedom of design. Studies are under way to explore the feasibility of using such structures as the backbone member for various structures and automobile parts. Fiber reinforced resin (FRP) structures which use a long continuous fiber strand are produced, as described in GB 2004835 for example, by impregnating a long continuous fiber strand (or roving) of glass fibers or carbon fibers with a resin such as an unsaturated polyester resin or epoxy resin, winding the impregnated fiber strand in a predetermined pattern, and subsequently hardening the resin in the fiber strand. When a steering wheel core member is made of the resin impregnated long continuous fiber strand by the procedure just described, the product core member exhibits the same degree of strength as a conventional core member made of iron. However, this technique permits the production of a steering wheel of notably lighter weight, because the resin impregnated fiber strand has a substantially lower density than that of iron.
The FRP structure so produced exhibits a high strength which is sufficient to enable the structure to endure forces exerted thereon in the direction of the length of the fiber, but exhibits no appreciable strength to endure the forces exerted thereon in the direction perpendicular to the length of the fiber. As a result, the branched portions of the structure, where the fiber strands are branched, do not have sufficient strength. When the branched parts are subjected to an external force, the difficulty which arises is that the individual fibers at the branched portions undergo separation.
The steering wheel structure is such that when it is exposed to an external force, a twisting torque and bending load are brought to bear on the branched portions which intervene between the spoke parts and the boss part. When the core member is formed of the aforementioned long continuous fiber strand, since voids occur in the branched portions between the parts corresponding to the spoke of the steering wheel and the part corresponding to the ring of the steering wheel and in the points of juncture of the spoke parts and the boss metal piece as a result of the manner of fabrication of the steering wheel, the steering wheel inevitably possesses insufficient torsional rigidity and bending rigidity and, as a result, the individual fibers which form the FRP yield to separation at the branched portions and in the points of juncture.
A need therefore continues to exist for a method of manufacturing an FRP structure of improved strength properties, particularly at vulnerable parts of the structure.